This invention relates to a wear resistant high strength rail utilized at a curved portion of a rail road, and more particularly a wear resistant high quality rail having a capability of preventing propagation of unstable rupture.
Rupture of a rail often results in a large train accident. Among the causes of the rupture include a shelling damage caused by the contact between the rail and a car wheel, cracks at the joints between rails, shatter cracks in the rail, large oxide contaminants and deep surface defects. When the rail is used over a long period of time, various cracks occur at various portions of the rail which result in transversal or longitudinal defects due to fatigue, and will propagate with time. Eventually, the defect reaches a specific rupture toughness value (for example K.sub.IC value specified by ASTM E399). As a consequence, a rapid unstable rupture occurs, thus breaking the rail. In a derail accident causing a large number of victims, when the end of a wear resistant alloy steel rail including cracks produced at the time of cutting with gas was examined. It was found that unstable rupture cracks induced by a shock load caused by the car wheel propagate over a length of more than 10 meters in the longitudinal direction in the web 11 of a rail 10 as shown in FIG. 5. Such cracks branch to the head 12 or foot 13, thus resulting in an accidental rupture.
In a prior art wear resistant rail utilized to prevent these defects, the wear resistance property of its head 12 contacting with the car wheel is constructed to have a fine pearlite structure having a higher strength than an ordinary rail.
Although such fine pearlite structure provides excellent wear resistant property, it is brittle so that its resistance to the generation of unstable rupture is low. For this reason, when using such a rail, it is necessary to always prevent the generation of surface and inside defects. Where there is a fear of generating such defects, it is necessary to periodically detect such defects by ultrasonic fault locater before the unstable rupture occurs so as to detect and remove defective portions.
Various measures have been tried to increase the resistance to generation of unstable rupture caused by fatigue and defects generated at specific portions of the rail such as, the web and the foot. These measures, however, are not always effective. In any case, it is necessary to always avoid the generation of defects and the propagation of unstable destructive cracks. Yet, such generation of defects and propagation thereof has not been avoidable in existing rails.